An attempt is usually made to minimize the thermoelastic deformations of the reflector or of the radiating panel in order to ensure stability of the directivity of the antenna. The thermoelastic deformations of the reflector or of the radiating panel originate from the cyclical thermal variations caused by passing in alternation through zones of shadow and zones of exposure to the solar rays.
In the rest of the text, item of transmitting equipment means the reflector or the radiating panel.
A thermal protection membrane is usually placed between an active face of the item of transmitting equipment and space in order to thermally insulate the item of transmitting equipment and limit the thermoelastic deformations. More particularly, these are multi-layer protective membranes comprising a stack of polyimide layers. The polyimide used is well known to those skilled in the art; it involves, for example, a layer of Kapton® (a brand of polyimide film registered to E. I. Du Pont de Nemours and Company) in which Germanium is deposited. This insulation is extremely light. Moreover, this insulation has the advantage of being generally transparent to the radio waves.
When the membrane is installed on a reflector, attempts are made to prevent the membrane sticking to the concave reflecting face of the reflector in order to prevent damage to the reflector because of the aerodynamic flows that heat its surface. When the membrane sticks to the concave face of the reflector, the Germanium focuses the solar rays, which has the effect of damaging the elements that are in the path of a ray reflected by the concave reflecting surface of the reflector such as, for example, a radiofrequency source or else a secondary reflector.
Usually the membrane is stretched between the concave face of the reflector or of the radiating panel and space and the periphery of the membrane is attached to the edge of the reflector separating the active surface from the inactive surface of the reflector or of the panel.
Because of their design in different materials, the membrane and the item of transmitting equipment sustain different expansions/retractions when the temperature varies.
This solution does not guarantee a permanent tension of the membrane because the antenna is subjected to temperature variations.
Moreover, at high frequency (Ka band), the Kapton® is not totally transparent to the radio waves. The membrane therefore induces phase shifts on the radiation reflected by a reflector or radiated by the radiating panel. The value of the phase shift depends on the positioning of the membrane relative to the active surface transmitting, that is to say reflecting or radiating, the radio waves.
Attempts are made to keep the membrane permanently stretched between the item of transmitting equipment and space so that the phase shift induced by the membrane is always the same.
There is a solution for ensuring a permanent tension of the membrane 1. This solution is shown in FIGS. 1a and 1b in the case of a dual-grid reflector, that is to say a reflector 2 comprising two individual reflectors 7, 9. It is based on the use of tensioners. Tensioners 6 are distributed evenly over the periphery of the reflector and are attached to the structure 5 connecting the two individual reflectors, that is to say separating the active-surface face 3 from the inactive surface 4 of the reflector. During the operation of attaching the membrane 1 to the reflector 2 using attachment means 8, the tensioners are folded in a U-shape between the membrane and the edge 5 of the reflector 2 so that they apply a force {right arrow over (E)} to the membrane towards the outside of the reflector which permanently stretches the membrane like a drum skin between the active face and space.
However, this solution involves a prolonged immobilization of the reflector when the tensioners are installed before the membrane is attached thereto.
Moreover, the operation of attaching the membrane to the reflector is complex and difficult to reproduce. During this operation, it is necessary not only to ensure that the tensioners are folded in a U-shape, but also that the folding is such that the membrane can be stretched like a drum skin.
Furthermore, this solution can be installed only on dual-grid reflectors; it cannot be installed on single reflectors or on radiating panels because the edge of these items of equipment separating the active surface from the inactive surface does not provide a smooth surface for the bonding.
One object of the present invention is to alleviate the aforementioned drawbacks.
Furthermore, this solution is bulky and fragile. The tensioners that are folded in a U-shape occupy a considerable space on the periphery of the reflector and the merest impact can unstick them or break them.
Another object of the invention is to remedy this drawback.